In the hot rolling of steel, for example, scale, i.e., an oxide film, is formed on the surface of the rolling material when rolling. If the rolling is performed while the scale is adhered to the surface, good surface properties of the rolling material cannot be maintained. Therefore, the removal of the scale is performed by a descaling system by spraying high pressure water onto the surface of the rolling material.
The descaling system includes, for example, multiple descaling headers spraying the high pressure water toward the rolling material, a pump supplying the high pressure water to the descaling headers, an electric motor driving the pump, and a valve. For example, the valve controls the opening/closing of a branch pipe for releasing the water supplied from the pump into a pit, etc., in the state in which the water is not sprayed from the descaling headers, etc.
Also, in the descaling system, multiple pumps and electric motors of the same rating are arranged in parallel; and the high pressure water is supplied to the descaling headers from the multiple pumps. For example, in the case where multiple pumps and/or electric motors of different ratings are used, the pressures at the output ends of the pumps are undesirably different. Also, if the pumps are connected in series, water of a constant pressure unfortunately can no longer be supplied because the pressure supplied is different due to the number of operating pumps.
If the operations of the electric motor and the pump are stopped undesirably in the state in which the water is not sprayed from the descaling headers, there is a risk that the necessary pressure cannot be obtained when performing the next spraying. Therefore, there is a descaling system in which the operations of the multiple pumps are continued at a constant rotation speed. In such a case, in the state in which the descaling headers are not spraying, the high pressure water is merely released to the branch pipe side by opening the valves to protect the pumps and/or the electric motors; and energy is undesirably consumed wastefully. It is necessary for the water sprayed from the descaling headers to have a high pressure; and it is necessary for the electric motors and/or the pumps to have a large capacity. Therefore, it is desirable to suppress the wasteful consumption of energy such as that recited above as much as possible.
For example, in Patent Document 1, the necessary water amount is predicted from the position information of the rolling material and the spray patterns of the descaling headers; the number of operating pumps is calculated based on the predicted water amount; and the operations of the pumps are controlled. From the calculation result, the pumps other than the necessary number of pumps are caused to standby at the standby speed until the next acceleration timing. Due to mechanical constraints, a constant amount of time is necessary until the pump switches from the standby operation to the high-speed operation. Therefore, the high-speed operation of the pump is started prior to the timing of the actual spraying by the amount of time necessary to reach the high-speed operation. Thereby, it is possible to operate the pumps at the necessary time and at the necessary rotation speed; and higher energy conservation of the descaling system is possible.